ES2655512T3 - Structure to be used in a corrosive environment - Google Patents

Abstract

A structure to be used in a corrosive environment, comprising: - a primary structural element (1), primary structural element (1) being made of metal and provided with a protective coating, protective coating having a composition comprising zinc with a content of at least 40% by weight relative to the weight of the protective coating, - a secondary structural element (2), secondary structural element (2) that is made of metal and is provided with a protective coating, protective coating that is an alloy comprising aluminum and manganese, an alloy in which the joint content of aluminum and manganese is at least 90% by weight with respect to the weight of the protective coating, an alloy comprising more aluminum than manganese by weight, and, in which the primary structural element (1) and the secondary structural element (2) are in electrical contact with each other.

Description

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

DESCRIPTION

Structure to be used in a corrosive environment

The invention relates to a metal structure that is suitable for use in a corrosive environment, for example a structure to be arranged outside.

When a metal structure is used in a corrosive environment, there is a risk that the structural integrity of the structure will be jeopardized by the corrosion of one or more of the structural elements that are part of the structure. For example, moisture can cause corrosion of the metal surfaces of structural elements that make contact with the wet environment directly. In addition to this corrosion due to contact with the wet environment itself, the arrangement of the metal structure in a wet environment can cause electrolytic corrosion of at least one of the structural elements, in particular when materials with a different composition for structural elements are used They make electrical contact with each other. The different composition may lead to a difference in galvanic potential between structural components that have a different material composition. The humidity of the humid environment can act as an electrolyte that closes the electrical circuit between the structural elements that make electrical contact with each other. The closed electrical circuit allows electrons to move from one structural element to another, thereby causing electrolytic corrosion.

It is known to provide metallic structural elements with a protective coating to provide a corrosion resistance of their surfaces that make direct contact with the corrosive environment, for example wet. Such protective coatings may be organic protective coatings, for example paint, or metal protective coatings. For example, structural elements made of steel can be provided with a protective zinc coating by galvanization.

The metallic protective coating materials that are used to coat structural elements are normally less noble than the substrate material, so that in case a galvanic cell is formed in the structural element itself, for example, due to a damaged protective coating , the protective coating is corroded instead of the substrate, so that the structural integrity of the structure is compromised, at least initially, to a lesser extent. This is called "cathodic protection."

However, the disadvantage of using a less noble protective coating material is that it can be affected by electrolytic corrosion when another structural element that is in electrical contact with the protective coating is of a nobler material. In particular, when a protective zinc coating is used to protect steel, this occurs frequently, since zinc is less noble than steel.

The "corrosion guides" published by the National Physical Laboratory of Middlesex, United Kingdom, in the series "corrosion control" comprise a volume called "bimetallic guide", which exposes electrolytic corrosion and related design problems. On page 4 of this "bimetallic guide", there is a table showing that zinc can be attacked by electrolytic corrosion if combined with aluminum or aluminum alloys.

Document DE 102007058716 deals with the mounting of a hyper-steel, such as chrome steel or chromonickel steel by means of hypoalloyed bolts. Due to the difference in corrosion potential, electrolytic corrosion will occur between hyper-welded steel and hypoalloyed steel if no additional measures are taken. Document DE 102007058716 proposes to provide an intermediate element between hyper-alloy steel and hypoalloyed steel, an intermediate element that is significantly less noble than hyper-alloy steel and comparable to hypoalloyed steel, or less noble than it. The intermediate element serves as a sacrificial anode for the hypoalloyed bolt.

However, a different situation occurs when two or more structural elements are used that are in electrical contact with each other, both structural elements that have to be provided with a protective coating to protect them from the environment in which they are arranged. In this situation, the material of the structural elements under the protective coating is not particularly relevant to the question of whether electrolytic corrosion will occur. The most important thing is the selection of protective coating materials. If protective coatings are not carefully selected, electrolytic corrosion can occur even in a situation where the structural elements are made of the same material.

From the point of view of avoiding electrolytic corrosion, it would be desirable to use the same protective coating material for both construction elements, but this is not always possible, for example if wear of the adhesive should be avoided. In addition, the use of elements such as sacrificial anodes is not always desired.

The object of the invention is to provide a structure that has resistance to electrolytic corrosion and that offers at least one alternative option of a combination of materials, in particular protective coating materials, compared to what is known in the prior art.

This object is achieved by a structure to be used in a corrosive environment, which comprises:

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

- a primary structural element, a primary structural element that is made of metal and is provided with a protective coating, protective coating having a composition comprising zinc with a content of at least 40% by weight with respect to the weight of the protective coating,

- a secondary structural element, secondary structural element that is made of metal and is provided with a protective coating, protective coating that is an alloy comprising aluminum and manganese, an alloy in which the joint content of aluminum and manganese is at least 90% by weight with respect to the weight of the protective coating, alloy comprising more aluminum than manganese by weight, and

in which the first structural element and the secondary structural element are in electrical contact with each other.

The inventors have discovered that a primary structural element that is made of metal and is provided with a protective coating having a composition comprising zinc (Zn) with a content of at least 40% by weight with respect to the weight of the protective coating, it can be combined in a corrosion environment with a secondary structural element that is also made of metal but has a protective coating that is an alloy comprising aluminum (Al) and manganese (Mn), an alloy in which the joint content of aluminum and Manganese is at least 90% by weight with respect to the weight of the protective coating, alloy comprising more aluminum than manganese by weight. If these two structural elements are in electrical contact with each other, and the structure of which the structural elements form a part is arranged in a corrosive environment, a good resistance against electrolytic corrosion is observed, even in a case where the environment corrosive be a moist saline environment.

Furthermore, it has been observed that the corrosion resistance for a combination of protective coating materials according to the invention is largely independent of the relative size of the surface areas of the primary and secondary structural elements.

Structural elements that are in electrical contact with each other means that the two structural elements are not electrically isolated from each other. For example, an electrical contact is present when there is a direct physical contact between the metal or metallic protective coating of the primary structural element and the metal or metallic protective coating of the secondary structural element. In another example, an electrical contact is present when the metal or metallic protective coating of the structural element is first connected to the metal or metallic protective coating of the secondary structural element by means of one or more conductive elements, for example by means of a metallic bolt or metal rings. In general, an electrical contact is present when a path is provided that allows electrons to move from the primary structural element (including its protective coating) to the secondary structural element (including its protective coating) or vice versa. This path does not have to be a closed loop in the structure, for example it is possible that the path can be closed due to the presence of an electrolyte, for example saline water.

In particular, good resistance to electrolytic corrosion has been observed when the aluminum content in the protective coating of the secondary structural element is at least about 75% by weight with respect to the weight of the protective coating.

Preferably, the aluminum content in the protective coating of the secondary structural element is at least about 75% by weight with respect to the weight of the protective coating, and at least about 80% by weight of the rest of the protective coating is manganese.

Preferably, the manganese content in the protective coating of the secondary structural element is between about 1% by weight and about 25% by weight, more preferably between about 5% by weight and about 18% by weight, with respect to protective coating weight.

Examples of compositions of the protective coating of aluminum and manganese are: approximately 81-83% by weight, for example 82% by weight, of aluminum, with respect to the weight of the protective coating and approximately 19-17% by weight, for example 18% by weight, of manganese, with respect to the weight of the protective coating; approximately 84-86% by weight, for example 85% by weight, of aluminum, with respect to the weight of the protective coating and approximately 16-14% by weight, for example 15% by weight, of manganese, with respect to to the weight of the protective coating; or about 94-96% by weight, for example 95% by weight, of aluminum, with respect to the weight of the protective coating and about 6-4% by weight, for example 5% by weight, of manganese, with regarding the weight of the protective coating.

Optionally, the protective aluminum and manganese coating of the secondary structural element consists of aluminum, manganese and unavoidable impurities.

The protective coating of aluminum and manganese alloy of the secondary structural element according to the invention also has good properties in terms of improving corrosion resistance against corrosion due to direct contact with the corrosive environment. The addition of manganese to aluminum has an effect

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

on the morphology of the protective coating layer. It results in a dense structure with small crystallites. The grain size is generally smaller than in a protective coating of pure aluminum that is deposited using an electrochemical deposition from an ionic liquid.

The dense morphology of the aluminum and manganese protective coating of the secondary structural element provides good protection for the substrate material, since it creates a tough barrier between the substrate and the environment.

The aluminum and manganese alloy used for the protective coating of the secondary structural element is less noble than steel, in particular less noble than the types of mild steel used, in general, in construction. Therefore, in the event that a secondary element is made of steel, and the protective coating of aluminum and manganese is damaged, the protective coating provides cathodic protection for the steel substrate of the secondary structural element.

Aluminum and manganese alloy is nobler than zinc protective coating or zinc containing the primary structural element. This contrasts with aluminum alloys such as aluminum and zinc alloys, aluminum and magnesium alloys, aluminum and tin alloys, or aluminum and silicon alloys, which are less noble than zinc.

Preferably, the thickness of the protective coating of the secondary structural element is between about 1.5 pm and about 100 pm, preferably between about 5 pm and about 30 pm.

In a possible embodiment, the metal of the primary structural element and / or of the secondary structural element is steel, for example mild steel. According to a commonly used definition, "mild steel" is the same as simple carbon steel.

In a possible embodiment, the metal of the primary structural element and / or of the secondary structural element is steel with a carbon content of 0.5% or less, optionally carbon steel with a carbon content of 0.5% or less .

In a possible embodiment, the metal of the primary structural element and / or of the secondary structural element is hypoalloyed steel, hypoalloyed steel which optionally contains 8% or less of linking elements.

In a possible embodiment, the metal of the primary structural element and / or the secondary structural element is steel, steel that is not stainless steel.

In one possible embodiment, the metal of the primary structural element or of the secondary structural element is carbon steel with a carbon content of 0.5% or less, and the metal of the other of the primary structural element and of the secondary structural element is steel. hypoalloyed, hypoalloyed steel that optionally contains 8% or less of linking elements.

Suitable protective coatings for the primary structural element include, for example, zinc protective coatings (for example, of the type indicated, in general, in the art, for example in the European standard in draft dEN10346: 2013, by "Z") , zinc and iron alloy protective coatings (for example, of the type indicated, in general, in the art, for example in the European standard in draft dEN10346: 2013, by "ZF"), zinc alloy protective coatings- aluminum (for example, of the type indicated, in general, in the art, for example in the European standard in draft dEN10346: 2013, by "ZA"), zinc-magnesium alloy protective coatings (for example, of the type to be indicates, in general, in the art, for example in the European standard in draft dEN10346: 2013, by "ZM") and protective coatings of aluminum-zinc alloy (for example, of the type indicated, in general, and n the technique, for example in the European standard in draft dEN10346: 2013, using “AZ”).

Examples of suitable protective coatings for the primary structural element include protective coatings that can be obtained by galvanizing (for example, batch galvanizing, hot dipping galvanization or electrogalvanization), Aluzinc® protective coatings, Magnelis® protective coatings and protective coatings of zinc having at least about 90% by weight pure zinc.

A possible protective coating material for the primary structural element is a hot-dip zinc (Z) protective coating, which can be applied on a first metal substrate by dipping the first metal substrate in a molten substance bath having a zinc content of at least about 99% by weight of the molten substance bath. In general, such a protective coating comprises approximately 99% by weight to approximately 99.9% by weight of zinc (with respect to the weight of the protective coating), the rest being, in general, aluminum and unavoidable impurities. By providing the first metal substrate with such a protective coating, a primary structural element according to the invention can be obtained.

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

A possible protective coating material for the primary structural element is a zinc-iron alloy (ZF) protective coating in hot bath, which can be applied to a first metal substrate by applying a zinc protective coating by dipping the first metal substrate in a bath of molten substance having a zinc content of at least about 99% by weight and a subsequent annealing that produces a protective iron-zinc coating with an iron content, usually from about 8% by weight to about 12 % by weight (with respect to the weight of the protective coating), the rest being mainly zinc. By providing the first metal substrate with such a protective coating, a primary structural element according to the invention can be obtained.

A possible protective coating material for the primary structural element is a zinc-aluminum alloy (ZA) protective coating in hot bath, which can be applied on a first metal substrate by immersing the first metal substrate in a molten substance bath which is composed of zinc and about 5% by weight of aluminum and small amounts of mischmetal. In general, such a protective coating comprises approximately 5% by weight of aluminum (with respect to the weight of the protective coating), the rest being, in general, zinc and the mischmetal. By providing the first metal substrate with such a protective coating, a primary structural element according to the invention can be obtained.

A possible protective coating material for the primary structural element is a zinc-magnesium (ZM) protective coating in hot bath, which can be applied on a first metal substrate by passing the first metal substrate through a molten zinc bath with a joint aluminum and magnesium content of about 1.5% by weight to about 8% by weight, the rest being mainly zinc. Such a protective coating generally comprises a combined aluminum and magnesium content of about 1.5% by weight to about 8% by weight (with respect to the weight of the protective coating), the remainder being mainly zinc. By providing the first metal substrate with such a protective coating, a primary structural element according to the invention can be obtained.

A possible protective coating material for the primary structural element is a hot-dip aluminum-zinc (AZ) alloy protective coating, which can be applied to a first metal substrate by immersing the first metal substrate in a molten substance bath that is composed of about 55% by weight of aluminum, about 1.6% by weight of silicon and the remainder zinc. In general, such a protective coating comprises approximately 55% by weight of aluminum, approximately 1.6% by weight of silicon (with respect to the weight of the protective coating) and the zinc moiety. By providing the first metal substrate with such a protective coating, a primary structural element according to the invention can be obtained.

A possible protective coating material for the primary structural element comprises about 2-8% by weight of aluminum, about 0-5% by weight of magnesium, about 0-0.3% by weight of linking elements, the bond being the Zinc residue and inevitable impurities. Such a protective coating comprises, for example, about 93.5% by weight of zinc, about 3.5% by weight of aluminum and about 3% by weight of magnesium.

Another possible protective coating material for the primary structural element comprises about 43% by weight of zinc, about 55% by weight of aluminum and about 1.5-2% by weight of silicon.

In general, a structure of the type to which the invention belongs comprises at least two types of structural elements. The first type of structural element comprises, for example, a beam, a profile, a rod, a strip and / or a metal sheet. Such structural elements form the frame of the structure and support the mechanical loads that are exerted on the structure. The second type of structural element comprises fasteners, brackets and the like (for example, bolts, nuts, screws, clips, clamps). They fasten the structural elements of the first type with each other by connecting them together. The structural elements of the second type can be used, alternatively or additionally, to connect other objects to the structural elements of the first type. Such objects could be, for example, solar panels, distribution boxes or other electrical equipment, cables and / or sensors or, for example, an exhaust system of a vehicle.

The primary structural element according to the invention can be a structural element of the first type or a structural element of the second type. The secondary structural element according to the invention can be a structural element of the first type or a structural element of the second type.

Optionally, the primary structural element according to the invention is a structural element of the first type and the secondary structural element according to the invention is a structural element of the second type.

Optionally, the structure according to the invention comprises a primary structural element according to the invention which is a structural element of the first type, which is connected with a structural element of the first type of a different material (for example, stainless steel or aluminum). In this possible embodiment, both structural elements of the first type are connected to each other by means of a structural element of the second type, which is a secondary element according to the invention. Such a structure could comprise, for example, a beam that is provided with a protective coating having a composition comprising zinc with a content of at least

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

40% by weight with respect to the weight of the protective coating, which is connected to a beam, for example, of stainless steel or aluminum by means of a bolt (or a bolt and a nut), bolt that is provided with a protective coating which is an alloy comprising aluminum and manganese, an alloy in which the joint content of aluminum and manganese is at least 90% by weight with respect to the weight of the protective coating, alloy comprising more aluminum than manganese by weight.

Optionally, the primary structural element according to the invention is a structural element of the first type and the secondary structural element according to the invention is also a structural element of the first type.

Optionally, the primary structural element according to the invention is a structural element of the second type and the secondary structural element according to the invention is a structural element of the first type.

Optionally, the primary structural element according to the invention is a structural element of the first type and the structure further comprises one or more secondary structural elements according to the invention that are a structural element of the first type, as well as comprising one or more structural elements. secondary according to the invention which are a structural element of the second type.

Optionally, the structure according to the invention comprises a primary structural element according to the invention which is a structural element of the first type and a secondary structural element according to the invention which is a structural element of the second type, and an object, for example a functional device, which is connected to the primary structural element by means of the secondary structural element. Such a structure could comprise, for example, a beam that is provided with a protective coating having a composition comprising zinc with a content of at least 40% by weight with respect to the weight of the protective coating, and an additional object (for example , a functional device such as a solar panel, a support for a solar panel, a distribution box or other type of electrical equipment, a cable and / or a sensor or, for example, a vehicle exhaust system) which is of a different material (for example, stainless steel or aluminum), an additional object that is connected to the beam with the zinc protective coating by means of a bolt (or a bolt and a nut) that is provided with a protective coating that is a alloy comprising aluminum and manganese, alloy in which the joint content of aluminum and manganese is at least 90% by weight with respect to the weight of the protective coating, and alloy comprising more aluminum q It was manganese by weight.

It has been observed that the corrosion resistance for the combination of protective coating materials according to the invention is largely independent of the relative size of the surface areas of the primary and secondary structural elements. Thus, the primary structural element may have a larger surface area than the secondary structural element, or the primary structural element may have a smaller surface area than the secondary structural element, or the primary structural element and the secondary structural element may have substantially the Same surface area. This is an additional advantage of the invention, since many known combinations of corrosion resistant protective coating material require that a combination protective coating material must be used for the structural element with greater surface area and that Use the other protective coating material of the combination for the structural element with smaller surface area.

In a possible embodiment, the primary structural element has a larger surface area than the secondary structural element. If electrolytic corrosion occurs in such an embodiment between the protective coatings of the primary and secondary structural elements despite the relatively high corrosion resistance of this combination of protective coatings, then the protective coating on the primary structural element would be affected. This is because the protective coating of the secondary structural element is slightly nobler than the protective coating of the primary structural element. However, since the primary structural element has a larger surface area, the corrosion will be more spread over the surface than if the primary structural element had a smaller surface area than the secondary structural element.

A structure according to the invention can be used, for example, as a mounting system for solar panels or it can be a part of such a mounting system. However, it can also be used in other structures, such as bridges, metal towers for power lines, cranes, support structures or in automotive applications, such as underbody or chassis or other parts of cars or trucks, or parts of other vehicles, for example motorcycles.

The structure according to the invention can be arranged or used in a corrosive environment, for example a humid environment, optionally a wet saline environment, for example outside, for example on land, or in a marine environment or a land in an area close to the sea. For example, the structure can be a support structure for solar panels or it can be used as a mounting system for solar panels or it can be part of such a mounting system, allowing solar panels to be arranged in a corrosive environment, for example in nearby areas to the sea or even in a marine environment, for example on board a ship or an underwater drilling rig. For example, the structure can be a vehicle or a part of a vehicle.

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

The protective coatings of the primary and secondary structural elements can be applied using procedures that are generally known in the art. Optionally, the protective coating of aluminum alloy and manganese is applied to the secondary structural element by means of electrodeposition from an ionic liquid. By using this procedure to apply the protective coating of aluminum and manganese, a dense layer of protective coating can be obtained with small crystals and few cracks or few gaps, or without them.

It is desirable that the protective aluminum and manganese coating of the secondary structural element adhere well to the substrate. It has been found that in the case that an electrodeposition from an ionic liquid is used to apply the protective coating of aluminum and manganese, it is advantageous to give the substrate on which the protective coating of aluminum and manganese will be applied a treatment prior by chemical attack, optionally by means of an electrochemical attack, optionally by means of an electrochemical attack in an ionic liquid.

The chemical attack strips the surface of the substrate, which results in a better adhesion of the protective coating on the substrate. The chemical attack also eliminates, for example, oxides or contamination of the substrate surface. This also improves the adhesion of the protective coating.

It is possible to carry out the electrochemical attack in the same type of ionic liquid as the ionic liquid in which the electrochemical deposition of the protective coating of aluminum and manganese took place. It is even possible to carry out the electrochemical attack in the same ionic liquid bath as the ionic liquid bath in which the electrochemical deposition of the protective aluminum and manganese coating takes place.

In a possible embodiment, a voltage in the range from about 0.5 V to about 1.5 V with respect to an aluminum electrode is used during the electrochemical attack, for example during a chemical attack time of about 1 second to about 90 seconds

In a possible embodiment, before carrying out the pretreatment of the substrate by chemical attack, the substrate is cleaned and / or degreased. This can be done, for example, by means of an acid, such as sulfuric acid.

In a possible embodiment, the ionic liquid is moved or otherwise agitated during the electrochemical deposition of the protective aluminum and manganese coating on the substrate to form the secondary structural element. This prevents the surface from being damaged due to an absence of reactive substances near the surface to form the protective coating.

In a possible embodiment, the ionic liquid is a combination of 1-ethyl-3-methylimidazolium chloride (EMIMCI) and aluminum chloride (AlCh), preferably in a molar ratio of about 1: 1.5, and further comprises MnCh, preferably between about 0.01% by weight and about 5% by weight of MnCl2, optionally between about 0.02 and about 1% by weight of MnCh, based on the weight of the ionic liquid.

In a possible embodiment, the current density during deposition of the protective aluminum and manganese coating is between about 2 A / dm2 and about 7 A / dm2, preferably about 4 A / dm2.

In a possible embodiment, the deposition process of the aluminum and manganese protective coating is carried out at a process temperature between about 45 ° C and about 100 ° C, optionally between 75 ° C and 95 ° C, optionally at approximately 90 ° C.

In a possible embodiment, the secondary structural element is cleaned after deposition of the protective aluminum and manganese coating, for example by water and / or acetone.

In a possible embodiment, the deposition time of the deposition of the aluminum and manganese protective coating is between about 1 minute and about 60 minutes, optionally between about 3 minutes and about 50 minutes, optionally between about 7 minutes and about 15 minutes, optionally between about 8 minutes and about 12 minutes, optionally about 10 minutes.

The invention will now be described in more detail with reference to the drawing, in which exemplary embodiments of the non-limiting form of the invention will be shown.

The drawing shows in:

Fig. 1: a first example of a structure according to the invention, Fig. 2: a second example of a structure according to the invention,

Fig. 3: an example of structures according to the invention that is used in a mounting system for a solar panel,

Fig. 4: a first image of the protective aluminum and manganese coating of the secondary structural element obtained by electrochemical deposition from an ionic liquid,

5

Fig. 5: a second image of the protective aluminum and manganese coating of the secondary structural element obtained by electrochemical deposition from an ionic liquid,

Fig. 6: results of accelerated electrolytic corrosion tests that have been carried out on different combinations of materials in a saline humid environment, shown as photographs of bolts in a profile,

Fig. 7: results of the accelerated electrolytic corrosion tests of fig. 6, profile pictures only,

Fig. 8: results of additional accelerated corrosion tests that have been carried out on bolts of 15 different materials.

Fig. 1 shows a first example of a structure according to the invention.

The structure of fig. 1 has a primary structural element 1, which in this example is a beam. It also has a secondary structural element 2, which is also a beam. The primary structural element 1 and the second structural element 2 are in electrical contact with each other. When the structure is arranged in a corrosive environment, for example wet, moisture will act as an electrolyte, closing the electrical circuit between the primary structural element 1 and the secondary structural element 2. If the moisture is saline, it will be an effective electrolyte, increasing the risk of electrolytic corrosion.

The primary structural element 1 and the secondary structural element 2 can be fixed together, for example by welding or by bolts, but this is not necessary as long as they make electrical contact with each other, 25 for example by electrically conductive structural elements.

Both beams are made of metal, for example steel, and are provided with a protective coating.

The protective coating of the primary structural element 1 is a metallic protective coating, a major component of which is zinc (Zn). The protective coating of the primary structural element comprises at least 40% by weight of zinc, based on the weight of the protective coating. The primary structural element 1 may have, for example, a zinc protective coating (for example, type Z according to the European standard in draft dEN10346.2013), a zinc-iron alloy protective coating (for example, type ZF according to the European standard in draft dEN10346: 2013), a protective zinc-aluminum coating (for example, type ZA according to the European standard in draft dEN10346: 2013), a protective coating of zinc-magnesium alloy (for example, type ZM according to the European standard in draft dEN10346: 2013) or a protective coating of aluminum-zinc alloy 35 (for example, type AZ according to the European standard in draft dEN10346: 2013).

The protective coating of the secondary structural element 2 is an aluminum and manganese protective coating, which means that the protective coating material is an alloy comprising aluminum and manganese. The protective coating comprises more aluminum than manganese by weight and the joint content of aluminum and manganese is at least 90% by weight with respect to the weight of the protective coating.

Preferably, the aluminum content in the protective coating of the secondary structural element 2 is at least about 75% by weight with respect to the weight of the protective coating. Optionally, at least about 80% by weight of the rest of the protective coating is manganese. For example, the aluminum and manganese protective coating of the secondary structural element comprises approximately 81-83% by weight, for example 82% by weight, of aluminum, with respect to the weight of the protective coating and approximately 19-17 % by weight, for example 18% by weight, of manganese, based on the weight of the protective coating; approximately 84-86% by weight, for example 85% by weight, of aluminum, with respect to the weight of the protective coating and approximately 16-14% by weight, for example, 15% by weight, of manganese, with with respect to the weight of the protective coating; or about 94-96% by weight, for example 95% by weight, of aluminum, with respect to the weight of the protective coating and about 6-4% by weight, about 5% by weight, of manganese, with regarding the weight of the protective coating.

Fig. 2 shows a second example of a structure according to the invention.

The structure of fig. 2 comprises two bands 4. These bands are primary structural elements, and are made of metal and are provided with a protective coating having a zinc content of at least 55 40% by weight with respect to the weight of the protective coating. For example, bands 4 are galvanized or

otherwise provided, for example, with a zinc protective coating (for example, type Z according to the European standard in draft dEN10346: 2013), a zinc-iron alloy protective coating (for example, type ZF according to the European standard in draft dEN10346: 2013), a protective zinc-aluminum coating (for example,

8

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

type ZA according to the European standard in draft dEN10346: 2013), a protective coating of zinc-magnesium alloy (for example, type ZM according to the European standard in draft dEN10346: 2013) or a protective coating of aluminum-zinc alloy (for example, type AZ according to the European standard in draft dEN10346: 2013).

The bands 4 are connected to each other by means of a bolt 5. The bolt is provided with a protective coating which is an alloy comprising aluminum and manganese, the protective coating comprising more aluminum than manganese by weight and the joint content of aluminum and Manganese is at least 90% by weight with respect to the weight of the coating. In the structure of fig. 2, bolt 5 is a secondary structural element.

Preferably, the aluminum content in the protective coating of the bolt 5 is at least about 75% by weight with respect to the weight of the protective coating. Optionally, at least about 80% by weight of the rest of the protective coating is manganese. For example, the bolt and aluminum manganese protective coating comprises approximately 81-83% by weight, for example 82% by weight, of aluminum, based on the weight of the protective coating and approximately 19-17% by weight , for example 18% by weight, of manganese, with respect to the weight of the protective coating; approximately 84-86% by weight, for example 85% by weight, of aluminum, with respect to the weight of the protective coating and approximately 16-14% by weight, for example 15% by weight, of manganese, with respect to to the weight of the protective coating; or about 94-96% by weight, for example 95% by weight, of aluminum, with respect to the weight of the protective coating and about 6-4% by weight, for example 5% by weight, of manganese, with regarding the weight of the protective coating.

Fig. 3 shows an example of structures according to the invention that are used in a mounting system for a solar panel, in a side view.

In the embodiment of fig. 3, a solar panel 10 is mounted on a support structure 8. The support structure comprises a first leg 20, a second leg 22 and an inclined beam 21 extending between the first leg 20 and the second leg 22. The inclined beam 21 is welded, in the present embodiment, to the first leg 20 and to the second leg 22 to form a porch. Although it is not visible in fig. 3, the support structure comprises a second portico similar to that constituted by the first leg 20, the inclined beam 21 and the second leg 22. This second portico is arranged next to the porch constituted by the first leg 20, the inclined beam 21 and the second leg 22.

The support structure 8 further comprises a lower band 23 and an upper band 24. The lower band 23 and the upper band 24 extend from the gantry constituted by the first leg 20, the inclined beam 21 and the second leg 22 to The second porch. The lower band 23 and the upper band 24 are arranged adjacent to the solar panel 10 and thereby prevent the solar panel 10 from sliding up or down on the inclined beam 21.

The lower band 23 and the upper band 24 are connected to the gantry constituted by the first leg 20, the inclined beam 21 and the second leg 22 and with the second gantry by means of bolts 30.

The support structure 8 further comprises at least one side plate 25. The side plate 25 is connected to the inclined beam 21 by means of a bolt 32 and to the solar panel 10 by means of a bolt 31. The side plate 25 prevents the solar panel from moving laterally on the inclined beam 21.

A cable 11 connects the solar panel 10 with a distribution box 12. The distribution box 12 is connected to the first leg 20 by means of a lower support profile 27 and an upper support profile 26. The upper support profile 26 and the lower support profile 27 are connected to the distribution box by means of bolts 33 and to the first leg 20 by means of bolts 34.

The cable 11 is attached to the first leg by means of a metal cable flange 35.

In the support structure 8 of fig. 3, the first leg 20, the second leg 22, the inclined beam 21, the second gantry, the lower band 23, the upper band 24, the side plate 25, the upper support profile 26 and the lower support profile 27 are structural elements of the first type. At least one of them, but preferably all of them are primary structural elements according to the invention. The first leg 20, the second leg 22, the inclined beam 21, the second gantry, the lower band 23, the upper band 24, the side plate 25, the upper support profile 26 and / or the lower support profile 27 meet the requirements of the primary structural element according to the invention if they are made of metal and provided with a protective coating having a composition with a zinc content of at least 40% by weight. Thus, for example, they are galvanized or otherwise provided, for example, with a zinc protective coating (for example, type Z according to the European standard in draft dEN10346: 2013), a zinc-iron alloy protective coating (for example, type ZF according to the European standard in draft dEN10346: 2013), a protective zinc-aluminum coating (for example, type ZA according to the European standard in draft dEN10346: 2013), a protective coating of zinc-magnesium alloy (for example, type ZM according to the European standard in draft dEN10346: 2013) or a protective coating of aluminum-zinc alloy (for example, type AZ according to the European standard in draft dEN10346: 2013).

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

In the support structure 8 of fig. 3, bolts 30, 31, 32, 33, 34 and metal flange 35 are structural elements of the second type. At least one of them, but preferably all of them are secondary structural elements according to the invention. The bolts 30, 31, 32, 33, 34 and / or the metal flange 35 meet the requirements of secondary structural element according to the invention if they are provided with a protective coating which is an alloy comprising aluminum and manganese as the main components, coating protector comprising more aluminum than manganese by weight and the overall content of aluminum and manganese is at least 90% by weight.

Preferably, the aluminum content in the protective coating of the bolts 30, 31, 32, 33, 34 and of the metal flange 35 is at least 75% by weight. For example, the protective aluminum and manganese coating of bolts 30, 31, 32, 33, 34 and of the metal flange 35 comprises approximately 82% by weight of aluminum and approximately 18% by weight of manganese, or approximately 85% by weight of aluminum and

about 15% by weight of manganese or about 95% by weight of aluminum and

approximately 5% by weight of manganese.

Optionally, the first leg 20, the second leg 22, the inclined beam 21, the second portico, the lower band 23, the upper band 24, the side plate 25, the upper profile 26 of support or lower support profile 27 of a protective coating containing at least 40% by weight zinc. Optionally, not all bolts 30, 31, 32, 33, 34 or / or the metal flange 35 are provided with a protective coating that is an alloy comprising aluminum and manganese as the main components, protective coating comprising more aluminum than manganese in weight and the whole content of aluminum and manganese is al

minus 90% by weight. However, the support structure 8 comprises at least one structural element

primary which is made of metal and which is provided with a protective coating having a composition comprising at least 40% by weight zinc, and at least one secondary structural element that is in electrical contact with this particular primary structural element, secondary structural element that is made of metal and is provided with a protective coating that is an alloy comprising aluminum and manganese as the main components, the protective coating of said secondary structural element comprising more aluminum than manganese and the joint content of aluminum and of manganese at least 90% by weight.

Figures 4 and 5 show images of the protective aluminum and manganese coating of the secondary structural element obtained by electrochemical deposition from an ionic liquid, as well as part of the method of claim 14. The images of Figures 4 and 5 have been obtained by an electron microscope. The fine and dense grain structure of the aluminum and manganese coating is clearly visible.

A structure according to the invention can be manufactured, for example, by a method according to claim 14, optionally according to a combination of claim 14 and dependent claims 15-22.

According to this process, a first metal substrate is provided with a protective coating comprising at least 40% by weight of zinc with respect to the weight of the protective coating. This can be done by methods known in the art, such as galvanization, for example, batch galvanizing, hot-dip immersion galvanization or electrogalvanization. Thus, a primary structural element according to the invention is obtained.

In addition, a second metal substrate is provided on which a protective coating that is an alloy comprising aluminum and manganese, alloy comprising more aluminum than manganese by weight and alloy in which the joint content of aluminum and manganese is of at least 90% by weight with respect to the weight of the protective coating.

Preferably, the second metal substrate is cleaned and / or degreased before the other steps of the process are carried out. Cleaning and / or degreasing can be carried out, for example, using an acid, for example sulfuric acid.

After the optional cleaning and / or degreasing, the second metal substrate is chemically attacked, optionally electrochemically, so that the surface of the substrate is also roughened and / or the contamination and / or oxides of the surface of the second substrate are removed .

The second metal substrate is disposed in an ionic liquid bath. This can be done either before or after the electrochemical attack. If the second substrate is disposed in the ionic liquid bath before the chemical attack, the chemical attack can be carried out in this ionic liquid bath in the form of an electrochemical attack.

After the chemical attack, the second substrate can be removed from the ionic liquid bath and transferred to a second ionic liquid bath, in which the deposition of the protective aluminum and manganese coating is applied. Alternatively, deposition of the protective aluminum and manganese coating on the second metal substrate can take place in the same bath in which the electrochemical attack took place.

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

Alternatively, it is possible that the chemical attack does not take place in an ionic liquid but, for example, in an aqueous solution. It is not necessary that the chemical attack be an electrochemical attack; alternatively it can be, for example, a chemical attack. In the event that the chemical attack does not take place in the ionic liquid from which the protective aluminum and manganese coating is deposited, the second metal substrate is disposed in the ionic liquid bath after the chemical attack.

In case an electrochemical attack is applied, the chemical attack can be carried out, for example, at a voltage in the range of about 0.5 V to about 1.5 V with respect to an aluminum electrode, for about 1 Up to about 90 seconds.

After the chemical attack, the protective coating of aluminum and manganese is applied to the second substrate. An aluminum and manganese source is provided and the protective coating is deposited by electrodeposition from an ionic liquid, which is, for example, a combination of 1-ethyl-3-methylimidazolium chloride (EMIMCl) and aluminum chloride ( AlCl3), and also comprises MnCl2. The molar ratio between 1-ethyl-3-methylimidazolium chloride (EMIMCl) and aluminum chloride (AlCh) is preferably between about 1: 1 and about 1: 2.5, more preferably about 1: 1.5. Preferably, the content of MnCh is between about 0.01% by weight and about 5% by weight, optionally between 0.02 and 1% by weight, based on the weight of the ionic liquid.

Optionally, the deposition takes place in water-free conditions, for example in an argon atmosphere. Such conditions are suitable, in particular, when a combination of 1-ethyl-3-methylimidazolium chloride (EMIMCl) and aluminum chloride (AlCl3) is used, which further comprises MnCl2 for depositing the protective coating of aluminum and manganese. from it.

Preferably, during the deposition of the protective coating of aluminum and manganese, the ionic liquid moves, for example, by stirring it. This ensures that sufficient reactive components are available to form the protective coating of aluminum and manganese around the surface of the second metal substrate.

It has been found that a suitable current density for the deposition process of the aluminum and manganese protective coating is between about 2 A / dm2 and about 7 A / dm2, preferably about 4 A / dm2.

Optionally, the thickness of the deposited protective coating of aluminum and manganese is between about 1.5 pm and about 100 pm, preferably between about 5 pm and about 30 pm.

After the deposition of the protective coating of aluminum and manganese, the second substrate has become a secondary structural element according to the invention.

After the deposition of the protective coating of aluminum and manganese, the second substrate is removed from the ionic liquid bath and optionally cleaned, for example, by acetone and / or water.

Optionally, the electrochemical attack of the second metal substrate and / or the electrodeposition of the protective aluminum and manganese coating on the second metal substrate takes place at a process temperature between about 45 ° C and about 100 ° C, optionally between about 75 ° C and about 95 ° C, optionally at about 90 ° C.

The connection of the primary structural element and the secondary structural element to each other, so that the primary structural element and the secondary structural element are in electrical contact with each other ends the manufacture of the structure according to the invention.

Optionally, the protective coating of the primary structural element is applied in one of the following ways:

- immersing the first metal substrate in a bath of molten substance having a zinc content of at least about 99% by weight,

- applying a protective coating by immersing the first metal substrate in a bath of molten substance having a zinc content of at least about 99% by weight and a subsequent annealing that produces an iron-zinc protective coating with an iron content, normally, from about 8% by weight to about 12% by weight with respect to the weight of the protective coating,

- immersing the first metallic substrate in a bath of molten substance that is composed of zinc and approximately 5% by weight of aluminum and small amounts of mischmetal.

- By passing the first metal substrate through a molten zinc bath with a combined aluminum and magnesium content of approximately 1.5% by weight to approximately 8% by weight.

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

- Immersing the first metal substrate in a bath of molten substance that is composed of approximately 55% by weight of aluminum, approximately 1.6% by weight of silicon and the remainder zinc.

Figures 6 and 7 show the results of accelerated cyclic electrolytic corrosion tests that have been carried out on different combinations of materials in a wet and saline environment.

The accelerated corrosion tests have been carried out as follows: a stainless steel bolt, a bolt with an aluminum and manganese protective coating according to the invention and various types of galvanized bolts were arranged in a profile provided with a protective coating of ZM type of about 93.5% by weight of Zn, about 3.5% by weight of Al and about 3% by weight of Mg.

The profile with the bolts was subjected to the following test cycle:

- 24 hours salt spray test according to ASTM_B 117, with 5% NaCl at 35 ° C,

- four days in a condensing water climate, each day having 8 hours at 40 ° C and a relative humidity of 95% and 16 hours at 20 ° C and a relative humidity of 75%,

- two days with room climate, at 20 ° C and a relative humidity of 65%.

This test cycle was repeated six times, so a total of six weeks of trials took place. A chemical analysis showed that the stainless steel bolt was made of type 304 stainless steel, which has approximately 18% by weight of Cr, approximately 8% by weight of Ni, approximately 2% by weight of Cu, approximately a 1.7% by weight of Mn, about 0.25% by weight of Si and about 0.25% of Mo as linkers. The supplier identifies it as DIN 916 stainless.

Galvanized bolts are identified in fig. 6 through the text on the respective bolt heads. The bolt indicated by “NORM 8.8” is galvanized according to EN ISO 4042 and EN 12329 as supplied by Eriks + Baudoin and Fabory. The protective coating on this bolt was approximately 19 pm thick and contained Zn, Al, Si and Ti.

The bolt identified "HBS 8.8U" is galvanized according to ISO 12329 supplied by Eriks + Baudoin and Fabory. The protective coating of this bolt was approximately 56 pm thick and contained Zn and Pb.

The identified bolt "CW 8.8" is galvanized. The protective coating on this bolt was approximately 7 pm thick and contained mainly Zn.

The bolt identified "JD 8.8" is electrogalvanized according to EN ISO 4042 and EN 12329. The protective coating on this bolt was approximately 7 pm thick and contained mainly Zn.

Fig. 6 shows the combination of the profile and bolt. Column A of fig. 6 shows the situation at the beginning of the test. Column B of fig. 6 shows the situation after one week and column C of fig. 6 shows the situation after six weeks, therefore, until the end of the test.

Fig. 7 shows the profile only. Photograph A of fig. 7 shows the profile near the hole in which the stainless steel bolt was present during the test. Photograph B of fig. 7 shows the profile near the hole in which the galvanized NORM bolt in batches was present during the test. Photograph C of fig. 7 shows the profile near the hole in which the galvanized HBS 8.8u bolt was present during the test. Photograph D of fig. 7 shows the profile near the hole in which the electrogalvanized JD 8.8 bolt was present during the test. Photograph E of fig. 7 shows the profile near the hole in which the bolt with the aluminum and manganese protective coating according to the invention was present during the test.

After the six-week complete test, the combination of the ZM coated profile and the stainless steel bolt showed a white corrosion of the ZM protective coating. The stainless steel bolt was unchanged.

After the six-week complete test, the combination of the ZM coated profile and the galvanized CW 8.8 bolt showed some white corrosion of the ZM protective coating, and the entire bolt was corroded and showed a lot of red oxide.

After the six-week complete test, the combination of the ZM coated profile and the galvanized HBS 8.8u bolt showed some white corrosion of the ZM protective coating, and the bolt showed quite a bit of red oxide and white oxides.

After the six-week complete test, the combination of the ZM coated profile and the galvanized NORM bolt in batches barely showed any white corrosion of the ZM protective coating, but the bolt was covered with white oxides.

5

10

fifteen

twenty

25

After the six-week complete test, for the combination of the ZM coated profile and the electrically galvanized JD 8.8 bolt, the bolt showed a lot of red oxide.

After the six-week complete test, the combination of the ZM coated profile and the bolt with the aluminum and manganese protective coating according to the invention showed no white corrosion or other degradation of the ZM protective coating. The bolt had some red oxide, but upon closer inspection it showed that this was only in places where the protective coating did not adhere to the bolt. Where the protective coating was present, no degradation of the protective coating was observed.

Fig. 8 shows the result of accelerated corrosion tests in which the bolts as such were subjected to a humid and saline environment. This test is primarily aimed at determining corrosion resistance due to direct contact with wet and saline environments. No electrolytic corrosion was induced in this test.

The test cycle and the types of bolts that were tested were the same as for the electrolytic corrosion test whose results show figures 6 and 7.

Column A of fig. 8 shows the situation at the start of the test. Column B of fig. 8 shows the situation after one week and column C of fig. 8 shows the situation after six weeks, therefore, until the end of the test. With respect to the protective aluminum and manganese coating according to the invention, it should be noted that only the upper part of the bolt, which is the part surrounded by the housing "a" in column C of fig. 8, was provided with the protective aluminum and manganese coating according to the invention.

The stainless steel bolt came out quite clean from this test. It was not affected by corrosion.

In addition, the bolt that was coated with the aluminum and manganese protective coating according to the invention came out of the test with hardly any corrosion, at least on the part of the bolt that was coated with the aluminum and manganese protective coating according to the invention. .

The galvanized bolt identified "HBS 8.8U" came out of the test with many white oxides on its surface.

The galvanized bolts identified “CW 8.8” and “JD 8.8” came out of the test covered with red oxide.

The galvanized bolt identified “NORM 8.8” came out of the test with white oxides on its surface, although less than those shown by the “HBS 8.8U” bolt.

Claims (14)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 55 1. A structure to be used in a corrosive environment, comprising: - a primary structural element (1), primary structural element (1) that is made of metal and is provided with a protective coating, protective coating having a composition comprising zinc with a content of at least 40% by weight with respect to to the weight of the protective coating, - a secondary structural element (2), secondary structural element (2) that is made of metal and is provided with a protective coating, protective coating that is an alloy comprising aluminum and manganese, an alloy in which the joint content of aluminum and Manganese is at least 90% by weight with respect to the weight of the protective coating, alloy comprising more aluminum than manganese by weight, and, wherein the primary structural element (1) and the secondary structural element (2) are in electrical contact with each other. 2. A structure according to claim 1, in which the metal of the primary and / or secondary structural element is steel, for example mild steel. 3. A structure according to claim 2, wherein the metal of the primary structural element (1) and / or of the secondary structural element (2) is steel with a carbon content of 0.5% or less, and / or wherein the metal of the primary structural element (1) and / or of the secondary structural element (2) is hypoalloyed steel, hypoalloyed steel that optionally contains 8% or less of linking elements. 4. A structure according to any of the preceding claims, wherein the structure further comprises a functional device, the functional device being connected to a primary structural element (1) by means of a secondary structural element (2), in which the functional device is, optionally, one of a solar panel, a distribution box, a cable, a sensor, an exhaust system. 5. A structure according to any of the preceding claims, wherein the aluminum content in the protective coating of the secondary structural element (2) is at least 75% by weight with respect to the weight of the protective coating and, optionally, at less than 80% by weight of the rest of the protective coating is manganese. 6. A structure according to claim 5, wherein the protective coating of the secondary structural element (2) comprises 81-83% by weight of aluminum and 19-17% by weight of manganese, with respect to the weight of the protective coating, or wherein the protective coating of the secondary structural element (2) comprises 84-86% by weight of aluminum and 16-14% by weight of manganese, with respect to the weight of the protective coating, or wherein the protective coating of the secondary structural element (2) comprises 94-96% by weight of aluminum and 6-4% by weight of manganese, with respect to the weight of the protective coating. 7. A structure according to any of the preceding claims, wherein the protective coating of the primary structural element (1) is a zinc protective coating having at least 90% by weight pure zinc, a zinc alloy protective coating - iron, a zinc-aluminum alloy protective coating, a zinc-magnesium alloy protective coating or an aluminum-zinc alloy protective coating, wherein, optionally, the protective coating of the primary structural element (1) is a protective coating by hot bath immersion. A method for manufacturing a structure according to any of the preceding claims, a process comprising: - provide a first metallic substrate, - providing the first metallic substrate with a protective coating having a composition comprising zinc with a content of at least 40% by weight with respect to the weight of the protective coating, thereby obtaining the primary structural element (1), 5 10 fifteen twenty 25 30 35 40 Four. Five fifty 55 - provide a second metal substrate, - arrange the second metal substrate in an ionic liquid bath, - chemically attack the second metal substrate, - provide a source of aluminum and manganese, - electrochemically depositing a protective coating from the ionic liquid on the second metal substrate, protective coating which is an alloy comprising aluminum and manganese, an alloy in which the joint content of aluminum and manganese is at least 90% by weight with respect to the weight of the protective coating, alloy comprising more aluminum than manganese by weight, thereby obtaining the secondary structural element (2) and, optionally, during this electrochemical deposition, stir the ionic liquid, - connect the primary structural element (1) and the secondary structural element (2) to each other, so that the primary structural element (1) and the secondary structural element (2) are in electrical contact with each other. 9. A method according to claim 8, wherein the ionic liquid is a combination of 1-ethyl-3-methylimidazolium chloride (EMIMCl) and aluminum chloride (AlCh), preferably with a molar ratio of 1: 1.5, and furthermore preferably comprises between 0.01% by weight and 5% by weight, optionally between 0.02% by weight and 1% by weight with respect to the weight of the ionic liquid. 10. A method according to any of claims 8-9, wherein the chemical attack of the second metal substrate and the electrochemical deposition of the protective coating of an alloy comprising aluminum and manganese are carried out in the same ionic liquid bath. 11. A method according to any of claims 8-10, in which the chemical attack of the second metallic substrate is an electrochemical attack, wherein, optionally, the electrochemical attack of the second metal substrate is carried out at a voltage between 0.5 V and 1.5 V with respect to an aluminum electrode, preferably for 1 second to 90 seconds. 12. A method according to any of claims 8-11, wherein the electrochemical deposition of the protective coating that is an alloy comprising aluminum and manganese has a process parameter that is the current density, current density that is between 2 A / dm2 and 7 A / dm2, preferably 4 A / dm2 13. A method according to any of claims 8-12, in which the protective coating of the primary structural element (1) is applied in at least one of the following ways: - immersing the first metal substrate in a bath of molten substance having a zinc content of at least 99% by weight, - applying a zinc protective coating by immersing the first metal substrate in a bath of molten substance having a zinc content of at least 99% by weight and a subsequent annealing that produces an iron-zinc protective coating with an iron content normally from 8% by weight to 12% by weight with respect to the weight of the protective coating, - immersing the first metal substrate in a bath of molten substance that is composed of zinc and approximately 5% by weight of aluminum and small amounts of mischmetal, - by passing the first metal substrate through a molten zinc bath with a combined aluminum and magnesium content of 1.5% by weight up to 8% by weight, - immersing the first metal substrate in a bath of molten substance that is composed of 55% by weight of aluminum, 1.6% by weight of silicon and the remainder zinc. 14. A method according to any of claims 8-13, wherein the material of the first metallic substrate and / or the second metallic substrate is steel with a carbon content of 0.5% or less. A method according to any one of claims 8-14, wherein the material of the first metallic substrate and / or the second metallic substrate is hypoalloyed steel, hypoalloyed steel which optionally contains 8% or less of linking elements.